The present invention relates to a method and an apparatus for recording optical information; and, more particularly, to a method and an apparatus capable of recording optical information at high density.
Optical recording techniques have been widely used in storing a large volume of information on an optical information recording medium, e.g., such an optical disc as CD-recordable (CD-R) or the like. Recently, there has been introduced a technique to record the optical information at a speed of or beyond 2 to 6 times the standard recording speed.
Recording of information on the optical disc is accomplished by irradiating a pulsed laser beam onto the rotating optical discbasedon a digital signal, which has been obtained by digitizing the information to be recorded, to thereby form pits thereon.
In order to form the pits on the optical disc based on the digital signal, a high intensity laser beam is irradiated onto the optical disc during a high level of the digital signal, the pits being formed as a result of the high intensity laser beam causing a change of states in the recording layer being irradiated therewith. During a low level of the digital signal, a low intensity laser beam required for tracking is irradiated onto the disc.
There is illustrated in FIG. 2 a conventional recording method comprising steps of generating a recording pulse while the digital signal corresponds to a high level during which a pit is formed, wherein the recording pulse includes a top pulse Ttop and a multiple pulse set Tmp1 to TmpN, N being an integer, following the top pulse Ttop; and irradiating a laser beam onto the optical information recording medium based on the recording pulse, thereby forming an optically detectable pit having a length corresponding to the first intensity level. In this conventional method, the pulses within the multiple pulse set Tmp1 to TmpN have not only the same pulse width but also the same pulse interval Lpd.
A high speed recording can be achieved by rotating an optical disc at an increased speed and reducing the period of a digital signal according to the rotational speed of the disc.
A digital versatile disc (DVD) capable of allowing a large volume of information to be recorded in a higher density than a compact disc (CD) has been recently introduced.
The conventional DVD is similarly shaped as the CD, i.e., a disc shaped, and can store about 7 times, i.e., 4.7 GB, as much information as the CD. Such a large information recording medium is expected to be a great contribution to the multimedia information society.
Further, as in the development of CDs, a DVD recordable (DVD-R) can not be omitted in the development of DVDs, and the present applicant has developed the DVD-R for a practical use. In the DVD-R, as in the CD-R, a pit is formed by irradiating a pulse shape laser beam onto the rotating optical disc based on the digital signal which has been generated by digitizing the information to be recorded.
Since, however, the DVD-R can store the optical information with a higher density in comparison to the CD-R, the conventional method and apparatus for recording optical information used for the CD-R can not be used. The use of the conventional method and apparatus for recording optical information used for the CD-R may result in a plurality of errors being recorded or the optical information may not get recorded at all.
For example, as a result of a track pitch, i.e., the minimum pit length of the DVD-R being smaller than that of the CD-R, an excessive thermal energy of the previous pit may influence the formation of the current pit, which, in turn, may prevent the pit from being formed at the required position, which may appear as a jitter during the reproduction of the optical information stored thereon.
It is, therefore, an object of the present invention to provide a method and apparatus capable of recording optical information correctly on an optical information recording medium with a high density.
In accordance with an aspect of the present invention, there is provided a method for recording optical information on an optical information recording medium based on a digital signal which has a first intensity level representing a period for forming a pit and a second intensity level representing a period for not forming the pit, the method comprising the steps of:
generating a recording pulse which includes a top pulse and a multiple pulse set following the top pulse while the digital signal corresponds to the first intensity level; and
irradiating a laser beam onto the optical information recording medium based on the recording pulse, thereby forming an optically detectable pit having a length corresponding to the first intensity level,
characterized in that pulse widths of pulses within the multiple pulse set are set to be sequentially smaller based on the distance from the top pulse.
In accordance with another aspect of the present invention, there is provided an apparatus for recording optical information on an optical information recording medium based on a digital signal which has a first intensity level representing a period for forming a pit and a second intensity level representing a period for not forming the pit, the apparatus comprising:
a recording pulse generator for generating a recording pulse which includes a top pulse and a multiple pulse set following the top pulse while the digital signal corresponds to the first intensity level, wherein pulse widths of pulses within the multiple pulse set are set to be sequentially smaller based on the distance from the top pulse; and
a light source for irradiating a laser beam with a pulse shape onto the optical information recording medium based on the recording pulse, thereby forming an optically detectable pit having a length corresponding to the first intensity level on the optical information recording medium.